Organic light-emitting diodes (OLEDs) are useful in a variety of applications such as discrete light-emitting devices, or as the active element of light-emitting arrays or displays, such as flat-panel displays in watches, telephones, laptop computers, pagers, cellular phones, calculators, and the like.
Conventional OLED display structures are built on substrates in a manner such that a two-dimensional OLED array for image manifestation is formed. Each OLED in the array generally includes overlying layers starting with a light transmissive first electrode formed on the substrate, an organic electroluminescent (EL) emission medium deposited over the first electrode, and a metallic electrode on top of the organic electroluminescent medium. When an electrical potential is placed across the electrodes, holes and electrons are injected into the organic zones from the anode and cathode, respectively. Light emission results from hole-electron recombination within the device.
The EL layer within a color OLED display device most commonly includes three different types of fluorescent materials that are repeated through the EL. Red, green, and blue regions, or subpixels, are formed throughout the EL layer during the manufacturing process to provide a two-dimensional array of pixels. Each of the red, green, and blue subpixel sets undergoes a separate patterned deposition, for example, by evaporating a linear source through a shadow mask. Linear source vacuum deposition with shadow masking is a well known technology, yet it is limited in the precision of its deposition pattern and in the pattern's fill factor or aperture ratio; thus, incorporating shadow masking into a manufacturing scheme limits the achievable sharpness and resolution of the resultant display. Laser thermal transfer has the potential to deliver a more precise deposition pattern and higher aperture ratio; however, it has proved challenging to adapt laser thermal transfer to a high throughput manufacturing line, which is necessary to warrant its use in the manufacture of cost-effective OLED display devices.
One effective way for depositing color emissive sites is to use a laser thermal transfer apparatus. In this apparatus, a donor is provided which has organic material that can include a dopant having a specific fluorescent dye. An example of such an apparatus is set forth in U.S. Pat. No. 5,688,551 by Littman et al. The donor with the desired organic material is placed into close proximity to the OLED substrate within a vacuum chamber. A laser impinges through a clear (to the laser wavelength) support that provides physical integrity to the donor and is absorbed within a light-absorbing layer contained atop the support. The conversion of the laser's energy to heat sublimates the organic material that forms the top layer of the donor sheet and thereby transfers the organic material in a desired subpixel pattern to the OLED substrate.
A problem with using laser thermal transfer is that is subject to deterministic errors caused by the operation of the laser thermal transfer apparatus. One specific challenge in converting computer aided design (CAD) files produced by the display designer into instructions for a laser thermal transfer deposition system is to manage this process such that the system deposits an organic medium upon a substrate in such a way as to enable the manufacture of a high quality OLED display. For deposition to occur, CAD files must be converted through a raster image processor (RIP) into a form of instructions that the LTT printhead controller and motion control system can understand and follow. Design rule checking of the CAD is essential to guarantee that the design can be manufactured on the targeted equipment. Further, to get optimum performance from the LTT system, compensation for real world machine performance limitations is critical.
There is a need for a way to convert display design information into LTT machine control instructions in such that the manufacture of high quality OLED displays is assured.